In typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient through a vessel and advanced through therein until the distal end thereof is at a desired location in the vasculature. A a guidewire and a dilatation catheter having a balloon on the distal end thereof are introduced through the guiding catheter with the guidewire sliding through the dilatation catheter. The guidewire is first advanced out of the guiding catheter into the patient""s coronary vasculature and the dilatation catheter is advanced over the previously advanced guidewire until the dilatation balloon is properly positioned across the lesion. Once in position across the lesion, the flexible, expandable, preformed balloon is inflated to a predetermined size with a liquid or gas at relatively high pressures, such as greater than about four atmospheres, to radially compress the arthrosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter may. be withdrawn from the patients vasculature and blood flow resumed through the dilated artery.
In angioplasty procedures of the kind described above, there may be injury to or restenosis of the artery, which either necessitates another angioplasty procedure, a surgical by-pass operation, or some method of repairing or strengthening the area. To strengthen the area and help prevent restenosis, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly called a stent, inside the artery at the lesion. The stent is expanded to a larger diameter for placement in the vasculature, often by the balloon portion of the catheter. Stents delivered to a restricted coronary artery, expanded to a larger diameter by a balloon catheter, and left in place in the artery at the site of a dilated lesion are shown in U.S. Pat. No. 4,740,207 to Kreamer and U.S. Pat. No. 5,007,926 to Derbyshire, the content of which is incorporated herein by reference. Palmaz et al., 156 Radiology 73 (1985) and U.S. Pat. No. 4,733,665 describe introduction of a stent over a balloon catheter (incorporated herein by reference). A preferred stent for use with this invention is shown in PCT Application No. 960 3092 A1, published Feb. 8, 1996, the content of which is incorporated herein by reference.
The present invention is particularly directed to improved arrangements for releasably covering the ends of the stent to prevent the stent ends from flaring and snagging to better facilitate delivery thereof.
The art referred to and/or described above is not intended to constitute an admission that any patent, publication or other information referred to herein is xe2x80x9cprior artxe2x80x9d with respect to this invention. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. xc2xa71.56(a) exists.
This invention concerns apparatus suitable for delivery of stents to body cavities. In general, stents are prosthetic devices which can be positioned within a body cavity, for example, a blood vessel of the body of a living human or in some other difficultly accessible place. The stent prosthesis is formed of a generally tubular body, the diameter of which can be decreased or increased. Stents are particularly useful for permanently widening a vessel which is either in a narrowed state, or internally supporting a damaged vessel. Such stents are typically introduced into the body cavity by use of a catheter. The catheter is usually of the balloon catheter type in which the balloon is utilized to expand the stent, which is positioned over the balloon, to place it in a selected location in the body cavity. The present invention is particularly directed to improved arrangements for releasably covering/securing/attaching the stent, particularly the ends thereof, to the catheter to prevent snagging of the stent ends and to facilitate delivery thereof. The stent is held in place on the catheter and kept from flaring upward at its end(s) by means of at least one removable end covering means, or sock/sleeve, over the stent, the stent having been fitted to the catheter over the balloon, as by crimping. Most specifically, this invention is directed to improved modifications to the subject matter of the Savin U.S. Pat. No. 4,950,227 which is incorporated herein by reference.
In particular, the invention is directed to an improved stent delivery system designed to securely hold a stent over the balloon on a catheter, via the sleeve arrangements, and to protect the stent from deformation, damage or premature release during delivery intraluminally, as well as snagging during transportation. It is also a purpose of the present invention to provide for easier and smoother removal of the sleeve retaining means. The stent is formed to its lowest geometrical diameter when loaded. In one embodiment, rings or coils are placed over the ends of the stent to retain them and hold them to the balloon beneath the sleeves (unexpanded), and preferably adhered thereto, with little or no relative movement between the ID of the stent and the OD of the balloon/catheter arrangement. The sleeves aid in retaining the stent and hold the stent to the balloon (unexpanded). The rings or coils are each preferably attached (adhered) to the elastomeric socks and the other end of the sleeves are respectively attached to the catheter. Since most stents which are deformed to a low diameter will increase in diameter somewhat after being deformed (spring back), the rings/coils prevent spring back and increase the friction fit between the stent and balloon. When the balloon under the stent is inflated, the stent pushes out of the rings/coils and the sleeves are pushed down the balloon cones to allow the stent to deploy.
An alterative embodiment provides for easier and smoother removal of the sock retaining means. In this embodiment the rings or coils are placed over the cone portion of the balloon beneath the socks and preferably adhered thereto. The sleeves aid in retaining the stent and hold the stent to the balloon (unexpanded) with little or no relative movement between the ID of the stent and the OD of the balloon/catheter arrangement. The rings or coils are each preferably attached (adhered) to the elastomeric socks or sleeves. One end of the sleeves cover the ends of the stent and the other end of the sleeves are respectively attached to the catheter. When the balloon under the stent is inflated, the rings/coils, which are positioned on the tapered cone portion of the balloon, are driven primarily axially, resulting in the sleeves being pushed/pulled down the balloon cones to allow the stent to deploy. The positioning of the rings/coils on the cones of the balloon allows for more of an axial force when the balloon inflates rather then a radial force which may be the case if the rings are positioned on the ends of the stent, which may have a flatter profile as apposed to the tapered profile of the cone portion. This allows for a steadier, smoother, more controlled removal of the sleeves. Since most stents which are deformed to a low diameter will increase in diameter somewhat after being deformed (spring back), the sleeves also somewhat prevent spring back and increase the friction fit between the stent and balloon.
In a different embodiment, a polymer tube may be formed into a spiral, as by cutting molding or extruding, except for about 1-2 mm on one end; its entire length need only be about 1-2 cm. The uncut portion of the spiral, i.e., the ring end is placed over the end of the stent to retain it as already described. The other end of the coil, a portion of which may be uncut also to form a ring is attached to the catheter.
Modifications to this embodiment include replacement of the plastic ring with a metal ring or coil and replacement of the sleeve/ring with a metal or plastic coil or coiled ribbon. Short balloon cone length and/or tension on the spiral can help the spiral move off the stent when the balloon is inflated.